I own the DT250-80. I don't have the V6 but did about 30 min comparison with V7506 in the store before I bought the Beyers.
To me The DT250 are more neutral, accurate and refined. V6/7506 have a high "wow" factor. Howver, if you listen for a bit longer you realize that V7506 sound colored compared to DT250. The bass of the Sonys although very deep can be out of proporton and look overblown on bass heavy music. The midrange is also less than ideal, DT 250 reproduces voices far better- very smooth creamy midrange. DT 250 sound a bit darker but not rolled off IMO. There isn't a feeling of a missing treble, just smooth highs. Beyers soundstage is also wider(not as spacious as with open cans but very good for aclosed ones) and imaging better.
All in all these are better cans and they should be considering their higher price.